Q-switched fiber laser based on saturable absorption of ferroferric-oxide nanoparticles

We demonstrate that ferroferric-oxide (Fe₃O₄) nanoparticles exhibit nonlinear saturable absorption property at 1.55 μm, and fabricate two filmy saturable absorbers by embedding the nanoparticles into a polyvinyl alcohol (PVA) film or polyimide (PI) film separately. In the Fe₃O₄-PVA (Fe₃O₄-PI) Q-switched fiber laser, the pulse repetition rate increases from 8.5 kHz (5.5 kHz) to 28 kHz (49 kHz) and the pulse duration decreases from 23.5 μs (47 μs) to 6 μs (3.5 μs) by varying the pump power from 25 mW (23 mW) to 150 mW (650 mW). Experiment results indicate that PI-based saturable absorbers can afford larger powers than PVA-based saturable absorbers, which can be attributed to the higher fusion point of the PI film.